1. Field of Invention
Exemplary embodiments of the present invention relate to a micromechanical electrostatic resonator, and more specifically, relate to a structure of a micromechanical electrostatic resonator suitable for a high frequency resonator having a vibration body which is formed on a substrate using a Micro Electro Mechanical Systems (MEMS) technique.
2. Description of Related Art
The advent of a worldwide highly developed information society facilitates the progress of communication and multimedia markets. For example, a cellular phone for personal use is spread or a new business using an internet medium comes into existence. Among them, the cellular phone which is called as a motive power for the information age has many functions other than a simple function as a telephone. For example, the cellular phone is evolving so as to transmit and receive at high-speed large-scale data such as high quality music or color moving pictures, in addition to voices, characters and pictures. In order to mount such previously non-existent functions, on the cellular phone or the like, ‘miniaturization and low weight’ of electronic components is required due to space limitations. Further, a tendency to miniaturize a case of the cellular phone begins to appear a restriction due to operation limitation, and thus it is considered that a demand for ‘thinning’ increases in future. Meanwhile, lately, a demand in a market for ‘high frequency’ according to large scale information begins to appear drastically. For example, a wireless LAN is fully spread, a Bluetooth product appears, and a public use of UWB (Ultra Wide Band) is approved in United States of America. In addition, a communication apparatus is used in various fields such as a vehicle sensor, a notebook personal computer and so on. In order to maintain high properties under such various environments, it is required for ‘high reliability’ which does not exist up to now.
As a way to attain various demands as described above, a MEMS (Micro Electro Mechanical Systems) technology is exemplified. The MEMS, that is, the micro electro mechanical system is a high value-added component which is created with ‘micromachining’ based on fine processing techniques of a semiconductor. Along with a circuit, a fine structure, a sensor, an actuator or an energy source can be integrated in a small size. Demands for wireless apparatuses such as the cellular phone, the wireless LAN, a wireless function mounted sensor increase, and thus studies of RF (Radio Frequency) MEMS in this field are expanded. The RF MEMS attracts attention as a technique which realizes the miniaturization of the RF circuit. That is, passive components of the RF circuit such as an antenna switchable switch, a RF filter or a resonator are fabricated using the RF MEMS techniques, and thus it is expected that a communication apparatus is led overall to be miniaturized and to have high performance.
A high frequency resonator which uses a related art RF MEMS technique includes a micromechanical electrostatic resonator in which the mechanical vibration of a vibration body is excited by an electrostatic force based on alternating-current (AC) power, and a change in capacitance due to the mechanical vibration of the vibration body is used. The related art includes, as the micromechanical electrostatic resonator, a comb teeth-shaped resonator in which electrodes having a comb teeth structure are arranged oppositely to be engaged with each other. See, for example, WILLLAM C. TANG, et al. “Laterally Driven Resonant Microstructures” Sensors and Actuators, 20 (1989) P. 25–32. In this resonator, since the electrode portion has a comb teeth structure, a surface area is wide and a relatively low drive voltage is used. Further, since displacement and a change in capacitor are linear, it is advantageous in that a linear response is obtained.
Further the related art includes, as ones which are currently suggested, a resonator in which electrodes are provided at left and right sides or upper and lower sides of a beam portion, and the AC power is supplied to the electrodes such that the vibration body, of which both ends are supported by the beam portion, vibrates. See, for example, W. -T. Hsu, et al. “Q-optimized lateral free-free beam micromechanical resonators,” Digest of Technical Papers, the 11th Int. Conf. on Solid-State Sensors and Actuators (Transducers'01), Munich, Germany, Jun. 10–14, 2001, pp. 1110–1113.
In addition the related art includes, a resonator in which a pair of electrodes are arranged oppositely to each other at both sides of an outer circumferential portion of a disk of which a center portion is supported and the AC power is supplied to the electrodes such that the disk vibrates in a high-order stretching mode. See, for example, J. R. Clark, et al. “High-Q VHF micromechanical contour-mode disk resonators,” Technical Digest, IEEE Int. Electron Devices Meeting, San Francisco, Calif., Dec. 11–13, 2000, pp. 399–402.
Among various micromechanical electrostatic resonators described above, in the micromechanical electrostatic resonator comprising a comb teeth electrode structure of which both ends are supported by the beam portion and other movable portions, vibration is caused by the bending of the beam portion. Thus, it is referred to as a bending mode (bending vibration) resonator. Further, in the micromechanical electrostatic resonator in which a pair of electrodes are arranged oppositely to each other at both sides of the disk, the stretching vibration of the disk is used. Thus, it is referred to as a stretching mode (stretching vibration) resonator.